intech-emg and evoked potentials in the operating room during spinal surgery (1)

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EMG and Evoked Potentials in the OperatingRoom During Spinal Surgery

Induk Chung and Arthur A. GrigorianGeorgia Neurosurgical Institute and Mercer University School of Medicine, Macon, GA,

USA

1. Introduction

EMG is an important clinical electrodiagnostic tool to assess function of neuromuscular tissue.It assesses spinal motor nerve roots and determines correct placement of hardware in surgicalprocedures, including cervical, thoracic, and lumbosacral spinal decompression,instrumentation, and fixation of spinal deformity. Evoked potentials provide information onvascular compromise of the spinal cord and nerves. Hence, concurrent recordings of EMG andevoked potentials can assess function integrity of the spinal cord and nerve more accurately. Inthis chapter, we will discuss application of EMG and evoked potentials in spinal surgery.

2. EMG recording techniques in the operating room (OR)

2.1 Recording electrodes

Surface, intramuscular, and subdermal needle electrodes are used to record EMG activity inthe OR. Surface electrodes may not be used because of their inability to detect neurotonicdischarges in spine surgery (Skinner et al., 2008). In addition, sweat causes electrodes todetach from the skin, preventing stable recording during lengthy surgery (Chung,unpublished data). Both intramuscular and subdermal needle electrodes are sufficient todetect neurotonic discharges (Skinner et al., 2008). Intramuscular needle electrodes mayhave an advantage to record EMG activity when the subcutaneous tissue is thick. Subdermalneedle electrodes (13 mm length and 0.4 mm diameter) are generally used to record EMG inthe OR, and we also routinely use subdermal needle electrodes in our practice.

2.2 Recording parametersEMG is a simple and reliable technique which does not interfere with the surgicalprocedure. It is important to use proper recording parameters to achieve EMG recordings toobtain high signal-to-noise ratio. Recommended parameters of routine free-run EMG arelow-frequency filter (LFF) of 20-30 Hz, high frequency filter (HFF) of 1-3 KHz, a gain of 500-5,000, a sensitivity of 50-500 µV, and a sweep speed of 10-200 msec per division (Toleikis etal., 2000; Bose et al., 2002; Chung et al., 2009). LFF of greater than 50 Hz and HFF of less than3 KHz should be avoided. Impedance of subdermal needle electrodes is recommended to beless than 5 K Ώ, for impedance greater than 5 K Ώ may mask real EMG activity. If impedanceof all electrodes is too high, ground electrode should be replaced. If a particular electrodegives high impedance, the electrode should be replaced.

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EMG Methods for Evaluating Muscle and Nerve Function326

2.3 Muscle group selections and electrode placement

EMG in spinal surgery should cover all nerve roots at risk innervated by surgical levels. Inroutine EMG, depending on the surgical levels and number of channels available, bipolarelectrodes (an active and a reference) are placed subdermally over the belly of each muscle

group of interest. Electrodes should be placed ~1 cm apart with care and secured with tapeto prevent dislodgement. EMG should be recorded from the bilateral muscle groups toincrease specificity of nerve root activation. If fewer channels are available in the monitoringequipment, an active electrode is placed in one muscle and a reference electrode is placed inother muscle. Multiple nerve roots can be monitored with this montage, but it may bedifficult to identify specific nerve root at risk. Table 1 indicates representative muscle groupsto be recorded during spinal surgery (Leppanen, 2008).

Cervical Muscle

C2, C3, C4 Trapezius, Sternomastoid

(spinal portion of the spinal accessory nerve)C5, C6 Deltoid, Biceps

C6 Triceps, Extensor Carpi Radialis

C7 Flexor Carpi Radialis

C8, T1 Abductor Pollicis Brevis, Abductor Digiti Minimi

Thoracic

T5, T6 Upper Rectus Abdominis

T7, T8 Middle Rectus Abdominis

T9, T10, T11 Lower Rectus Abdominis

T12 Inferior Rectus Abdominis

Lumbar

L2, L3, L4 Vastus Medialis, Adductor Magnus

L4. L5, S1 Vastus Lateralis, Tibialis Anterior

L5, S1 Proneous Longus, Gastrocnemius

Sacral

S1, S2 Gastrocnemius

S2, S3, S4 External anal sphincter

Table 1. Representative muscle groups innervated by the cervical, thoracic, lumbar, andsacral nerve roots.

3. EMG recording

3.1 Neuromuscular junction (NMJ) recordingBlockade of NMJ significantly attenuates motor activity. Short acting muscle relaxants maybe used to facilitate intubation, but long acting muscle relaxants should be avoided. If pre-existing nerve root injury should be identified, succinylcholine, an NMJ blocking agent, isrecommended to use. However, succinylcholine should not be used for patients withmalignant hyperthermia (Minahan et al., 2000).

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EMG and Evoked Potentials in the Operating Room During Spinal Surgery 327

There are electrical stimulation techniques to monitor status of NMJ, and these are singletwitch, train-of-four (TOF) twitch ratio, tetanus, post-tetanic stimulation, and pulse ordouble burst technique (Leppanen, 2008). TOF twitch ratio is routinely used during surgery.Electrical stimulation (stimulation frequency of 1 Hz, duration of 300~500 msec, and

intensity of 10~40 mA) is delivered to a peripheral nerve 4 times, and 4 resulting compoundmuscle action potentials (CMAPs) are recorded. TOF is monitored from the thenar eminencefollowing stimulation of the median nerve, the abductor pollicis brevis followingstimulation of the ulnar nerve at the wrist, the tibialis anterior following stimulation of theperoneal nerve at the knee, or the abductor hallucis following stimulation of the posteriortibial nerve. It is recommended that TOF should be monitored in a muscle of the extremitywhere EMG activity is being monitored (Minahan et al., 2000; Leppanen, 2008). Four of fourtwitch ratio is obtained if less than 75% of NMJ is blocked. Three of four twitch ratio isobtained with 75% blockade, 2 of 4 with 80% blockade, and 1 of 4 with 90% blockade. Notwitch is obtained if 100% of NMJ is blocked (Leppanen, 2008). It is not desirable to usemuscle relaxants during surgical procedures where direct stimulation of pedicle screws andnerve roots are required (Minahan et al., 2000).

3.2 Free-run EMG

The dorsal and ventral roots spit into rootlets and minirootlets. The nerve root issusceptible to mechanical injury at the area that the split is present. The axons at this pointare enclosed by a thin root sheath and cerebrospinal fluid meninges, but lack epineurimand perineurim. Hypovascularity at the junction of the proximal and middle 1/3 of thedorsal and ventral roots place nerve roots more susceptible to injury (Berthold et al.,1984). Intraoperative free-run EMG is utilized to detect motor nerve root compromiseduring decompression for spinal stenosis and spondylosis, correction of spinal deformity,

radiculopathy secondary to disc herniation, and removal of tumor involving neural tissuein anterior and posterior surgical approaches (Holmes et al., 1993; Beatty et al., 1995;Maguire et al., 1995; Welch et al., 1997; Balzer et al., 1998; Toleikis et al., 2000; Bose et al.,2002; Chung et al., 2011).To determine any pre-existing nerve root injury, baseline EMG recording is made beforesurgery starts. EMG recording is then made continuously throughout the surgicalprocedure. Pre-existing nerve root injury will be shown as spontaneous activity with lowamplitude and periodic activity, whereas a normal free-run EMG response is absence ofactivity. If small amplitude, low frequency, or isolated discharge occurs at times which donot correlate with surgical manipulation of nerve roots, the EMG may not be pathologic.Mechanically elicited activity is characterized as polyphasic or a burst pattern consisting ofsingle or nonrepetitive asynchronous potentials (Fig. 1A). Tonic or train activity consistingof multiple or repetitive synchronous discharges may last for several minutes (Fig. 1B).Burst potentials are associated with direct nerve trauma such as tugging, displacement, freeirrigation, electrocautery, and application of soaked pledgets, but may not be associated

with neural insult. Train activity is related to sustained traction and compression of nerveroots, and it is more associated with neural injury. When these patterns occur, the surgeonshould be notified and corrective maneuver should occur. Audio and visual signalrecognitions are available in most monitoring equipment. For communication with theoperating surgeon, it is recommended to use audio signal through loud speakers forimmediate feedback.

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A

B

Left Vastus lateralis

Tibialis anterior

Gastrocnemius

Right Vastus lateralis

Tibialis anterior

Gastrocnemius

Left Vastus lateralis

Tibialis anterior

Gastrocnemius

Right Vastus lateralis

Tibialis anterior

Gastrocnemius

Fig. 1. Free-run EMG. EMG activity was recorded from the vastus lateralis, tibialis anterior,and gastrocnemius muscles during posterior spinal decompression. Bursts (A) andprolonged trains (B) of EMG activity are present in the left tibialis anterior muscle duringdecompression of nerve roots. Sensitivity 100 µV, time base 2 sec.

3.3 Stimulated EMG3.3.1 Monitoring segmental motor nerve root functionSegmental nerve root monitoring involves monitoring of function of the motor unit axon.This is achieved by recording free-run and electrically stimulated EMG activity from themuscle fibers of the motor units. When EMG activity is recorded with needle electrodes, theactivity recorded may be the result of activation of only a few motor units innervating thatmuscle. Other motor units may be activated, but this activation will go undetected becauseof the location of the recording electrodes. A monopolar EMG needle records the summatedactivity of 9 to 17 muscle fibers (Leppanen, 2008).Motor nerve root stimulation technique is applied when motor axons and non-neural tissue(tumor, scar) should be identified and differentiated between motor and sensory roots.

When scar tissue is present from previous surgical procedures, electrical stimulation canidentify where the motor axons lie within the scar tissue. The direct nerve root stimulationtechnique is also used to determine a degree of decompression of compressed nerve roots. Anerve root is stimulated using an insulated ball-tip probe, and a reference needle electrodeplaced around the site of incision. The current (duration of 0.1 msec, frequency of 1-3 Hz) isgradually increased until stimulus evoked EMG responses or CMAPs are recorded from themuscle innervated by the nerve root. Stimulation threshold should not be greater thanseveral milliamperes for uninjured motor nerve roots when neural tissue is directlystimulated. If tumor or scar is stimulated and threshold is greater than this value, viableneural tissue lies within the tumor or scar or no neural tissue is involved (Holland et al.,1998; Leppanen, 2008).

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Fig. 2. Placement of pedicle screws. Screws are placed within the pedicle (A), close to the

medical wall of the pedicle (B), or breach the cortex to make a direct contact with a nerveroot (C).

Fig. 3 is a representative trace of CMAPs following stimulation of a pedicle screw. CMAPswere recorded mostly from the right vastus lateralis and tibialis anterior muscles with astimulation threshold of 17 mA, indicating that the pedicle screw was placed securely withinthe pedicle bone.

LeftVastus lateralis

Tibialis anterior

Gastrocnemius

RightVastus laterlais

Tibialis anterior

Gastrocnemius

Fig. 3. CMAPs were elicited following electrical stimulation of the pedicle screw. EMG wasrecorded from the bilateral vastus lateralis, tibialis anterior, and gastrocnemius muscles.Current (duration of 0.2 msec, frequency of 1 Hz) was slowly increased to right L4 pediclescrew head via monopolar ball-tip probe. CMAPs were recorded mostly from the rightvastus lateralis and tibialis anterior muscles at the current threshold of 17 mA. Sensitivity200 µV, timebase 0.1 sec.

3.3.2.3 Evaluation of cervical pedicle screws

C5 nerve root palsy is most commonly attributed to direct nerve root injury secondary tomanipulation or traction of the nerve root and a segmental spinal cord injury secondary to

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1985). SSEPs are used to assess the functional status of somatosensory pathways duringsurgical procedures which affect peripheral nerve or plexus (Prielipp et al., 1999; Chung etal., 2009), spinal cord (deformity correction, traumatic spinal fracture, tumor removal,Duffau, 2008), and brain (carotid endarterectomy, aneurysm repair, Friedman et al., 1991;

Lam et al., 1991).For upper extremity SSEP recordings, cortical (C3, C4 of the international 10-20 system,reference to Fz) and subcortical SSEPs (cervical spinous process, reference to Fz) aremonitored upon alternate stimulation of the median or ulnar nerve at the wrist (stimulationintensity of ~20 mA, stimulation frequency of 3.1 Hz, stimulation duration of 0.5 msec)through surface electrodes (Fig. 4, left panel). For lower extremity SSEP recordings, cortical(Cz, reference to Fz) and subcortical SSEP (cervical spinous process, reference to Fz) aremonitored upon alternate stimulation of the posterior tibial nerve at the ankle or peronealnerve at the popliteal fossa (stimulation intensity of ~30 mA, stimulation frequency of

Fig. 4. Representative traces of SSEPs. Traces on the left column are upper-extremity SSEPsrecorded from C3, C4 for cortical response and C5 spinous process for subcortical responsefollowing alternate stimulation of the ulnar nerve at the wrist (Timebase 50 msec). Lower-extremity SSEPs are shown in the right column. SSEPs were recorded from Cz and C5spinous process following alternate stimulation of the posterior tibial nerve at the ankle(Timebase 100msec). The number of averaged samples, latency (msec), and amplitude (µV)are indicated in the trace. Parentheses indicate interpeak latency and interpeak amplitude.

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3.1 Hz, a stimulation duration of 0.5 msec) through surface electrodes (Fig. 4, right panel). Afew hundreds of samples (sampling rate of 8 kHz) are required to average to increase asignal-to-noise ratio. Signals were amplified (gain of 5,000~20,000) and filtered (LFF of 30Hz, HFF of 300 Hz,). Impedance of electrodes should be ~5 KΩ. All of these electrical

connections are grounded at patient’s shoulder (Balzer et al., 1998; Chung et al., 2009).

4.2 Motor evoked potentials (MEPs) and recording techniqueMEPs assess functional integrity of the anterolateral column of the spinal cord. MEPsprovide information about long tract function, segmental interneurons, and anterior graymatter function. Epidural stimulation of the spinal cord and transcranial electrical (TES) ormagnetic stimulation (TMS) of the motor cortex of the brain are the techniques used toobtain MEPs. TES is the most favorite technique utilized in the OR (McDonald, 2002, 2006).TES technique involves eliciting CMAPs after transcranial electrical stimulation of motorarea at 1~2cm anterior to C3 and C4, referenced to C4 and C3 (Calalncie et al., 1998; Chunget al., 2011) or C1 and C2, reference to C2 and C1 (Bose et al., 2004; Drake et al., 2010). For

electrical stimulation, an internal or external stimulator can be used. Some monitoringequipment has its own internal stimulator. An external cortical stimulator is also used forthis purpose. DigitimerTM D185 Multipulse stimulator (Digitimer Ltd., Welwyn Garden City,UK) is the only FDA approved stimulator for this clinical use. It has capabilities to controlinter-stimulation interval (ISI) and stimulation intensity up to 1,000 volts. Multipulsestimulation technique (4~6 repetitive stimulations and ISI of 1~2 msec) is usually applied(Calalncie et al., 1998; Bose et al., 2004; Drake et al., 2010; Chung et al., 2011). Stimulationthresholds range between a few hundreds and several hundreds of volts to elicit CMAPsdepending on pathophysiological status of the spinal cord, depth of anesthesia, and bonethickness. Evoked CMAPs are recorded from the muscles of upper and lower extremities asindicated in Table 1.

Representative traces of MEPs are shown in Fig. 5. After TES, evoked CMAPs were recordedfrom the muscles of upper and lower extremities during placement of thoracic pedicle screws.Stable CMAPs were present in all the muscles during pedicle screw placement, and the patientdid not develop new postoperative complication. We have been routinely testing MEPs duringall cervical and thoracic spine surgery for the past over ten years, and the presence of stableMEPs is the most reliable indicator to assess cervical and thoracic spinal cord and nerve rootfunction, instead of stimulation of mass and pedicle screws (Chung, unpublished data).There are safety concerns to test MEPs for patients. High voltage transcranial electricalstimulation causes jaw movement, resulting in tong laceration and mandibular fracture in0.2% of the patients undergoing TES. Bite blocks should be placed to prevent thesecomplications. MEPs should not be tested for patients with pre-existing history of seizure,intracranial injury, or presence of intracranial metal implants (McDonald, 2002, 2006).

4.3 Dermatomal somatosensory evoked potentials (DSSEPs) and recording technique

Researchers have demonstrated that SSEPs increase specificity of EMG during lumbosacral(Holmes et al., 1993; Balzer et al., 1998; Chung, unpublished data) and anterior spine surgery(Chung et al., 2011). However, one can argue that SSEPs can not detect injury in a singlenerve root because multiple nerve roots contribute to generate SSEPs. Dermatomalsomatosensory evoked potentials (DSSEPs) are suggested to use when assessing function ofindividual nerve roots. Stimulation is achieved with paired patch paste skin electrodeplaced 3-4 cm apart at dermatomal sites such as L3 at anterior mid-thigh, L4 at medial

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Left RightAbductor pollicisbrevis/Abductor digiti

minimi

External analsphincter

Vastus lateralis

Tibialis anterior/Gastrocnemius

Abductorhallucis

Fig. 5. MEPs were obtained after transcranial electrical stimulation (325V, ISI of 2 msec, 5repetitive pulse trains). CMAPs were recorded from the abductor pollicis brevis/abductordigiti minimi, external anal sphincter, vastus laterlais, tibialis anterior/gastrocnemius, andabductor hallucis muscles bilaterally. Timebase 100 msec, 100msec, vertical scales 50-200 µV.

midcalf, L5 at the dorsum of the foot, and S1 at the lateral aspect of the foot. Responses arerecorded from cervical spinous process. Recording parameters are stimulation intensity of~40 mA, duration of 0.3 msec, frequency of 5.1 Hz, LFF of 30 Hz, and HFF of 1 KHz. Eachtrial usually consists of 500 samples (Tsai et al., 1997). Clinical efficacy of intraoperativeDSSEPs appears controversial. DSSEPs are sensitive to detect nerve root compression andmechanical manipulation, but insensitive to nerve root decompression. DSSEPs can detect amisplaced pedicle screw only when the screw directly contacts and mechanically injures anerve root (Toleikis, 1993). DSSEPs are difficult to record and often require averaging ~500samples to increase a signal-to-noise ratio, indicating that DSSEPs can not detect mechanicalinsult immediately. Even with averaging more samples, Tsai and colleagues (1997) couldobtain baseline in only 57.6% of the patients. Hence, it is suggested that DSSEPs may be anadjunct to improve the sensitivity and specificity for detecting individual nerve injury whenfree-run and/or stimulated EMG is concurrently recorded.

4.4 Clinical efficacy of SSEPs and MEPs

Research for over the past three decades supports that SSEPs can detect and prevent spinalcord injury in cervical and thoracic, lumbosacral spinal surgeries. No quadriplegia resultedin a group of 100 patients with SSEP monitoring, compared with 8 quadriplegic patientsfrom a group of unmonitored 218 patients (Epstein et al., 1993). Five patients with persistentSSEP changes were associated with postoperative motor deficit among 20 patientsundergoing cervical and thoracic intramedullary cervical cord tumor removal (Kearse et al.,1993). SSEPs could detect ischemia in 44 out of 210 patients undergoing anterior cervicalsurgery. With simultaneous monitoring of SSEPs and EMG during posterior lumbar spinal

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fusion, bursts and trains of EMG activity were associated with a concurrent decrease inamplitudes of SSEPs (Chung, unpublished data).However, SSEPs may not be sensitive to predict postoperative clinical status in anteriorcervical spine surgery. Significant SSEP amplitude changes were observed in 33 out of 191

patients, and 50% of the patients developed postoperative neurological deterioration inanterior and/or posterior cervical spinal surgery (May et al., 1996). In a study with 871patients undergoing anterior cervical deformity surgery, 26 patients had significant SSEPchanges, and only 5 patients had postoperative neurological deficit (Leung et al., 2005). In508 patients undergoing anterior cervical discectomy and fusion (ACDF) with corpectomy, 8patients had postoperative deficits with preserved SSEPs (Khan et al., 2006). Seven patientsdeveloped new postoperative neurological deficit with preserved SSEPs in 758 patientsundergoing ACDF. SSEPs showed 35% sensitivity and 100% specificity to predictpostoperative neurological functions (Chung et al., 2011). A retrospective study with 1,055patients demonstrated that SSEPs had a sensitivity of 52% and a specificity of 100% topredict postoperative neurological status in cervical spine and spinal cord surgery (Kelleher

et al., 2008). Quadriparesis and paraplegia still resulted in patients with preserved SSEPs inanterior cervical fusion (Ben-David et al., 1987; Bose et al., 2004; Smith et al., 2007; Taunt etal., 2005).Simultaneous monitoring of SSEPs and MEPs has proven that MEP monitoring is morereliable than SSEP monitoring to predict postoperative motor deficits. Hillbrand andcolleagues (2004) reported that 12 out of 427 patients undergoing cervical surgery hadsubstantial or complete MEP loss. Ten patients restored MEPs with surgical intervention,and did not develop new postoperative deficit. Two patients with persistent MEP lossdeveloped new postoperative motor weakness. This study claimed that MEP monitoringshowed 100% sensitivity and 100% specificity to predict postoperative neurological status,

whereas SSEP monitoring had 25% sensitivity and 100% specificity (Hillbrand et al, 2004).Six patients with persistent MEP loss had new postoperative deficits, whereas significantSSEP loss without MEP changes observed in 2 patients did not have postoperative deficit in69 intracranial and spinal surgeries (Weinzierl et al., 2007). MEPs were also more sensitivethan SSEPs for detection of ischemia. MEPs were lost due to fluctuating blood pressure, andan increase in the mean arterial pressure above 90 mmHg restored them in 1 patient, butSSEPs were preserved during the entire surgical course in this patient (Wee et al., 1989).MEPs were superior to SSEPs for detection and prediction of postoperative neurologicalstatus. Whereas MEPs showed 100% sensitivity and 77% specificity, SSEPs had 35%sensitivity and 100% specificity to predict postoperative neurological outcomes in 758patients receiving ACDF (Chung et al., 2011).

5. Anesthesia

Although EMG is minimally sensitive to anesthesia, muscle relaxants should not be usedduring EMG recordings (Minahan et al., 2000). Evoked potentials, especially MEPs arehighly sensitive to anesthesia, but monitoring was still feasible withpropofol/fentanyl/nitrous oxide and partial neuromuscular blocking agents. In animalstudies, inhalant anesthetics significantly increased onset latency and amplitudes of MEPs(Haghighi et al., 19990a, 1990b, 1996). Under general anesthesia with fentanyl/propofol/nitrous oxide, 20% and 40~60% nitrous oxide attenuated MEPs by 40~60% and 50~70%,respectively (vanDongen et al., 1999), and 66% of nitrous oxide completely abolished MEPs

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(Zentner & Ebner, 1989). Narcotics were also shown to depress MEPs. Followingadministration of equipotent intravenous bolus of fentanyl, alfentanil, or sufentanil,amplitudes of MEPs were decreased to 34%, 43%, and 53% of baseline values, respectively(Thees et al., 1999). Total intravenous anesthetic or TIVA technique comprising remifentanil

with minimally depressive agents such as ketamine and etomidate improved MEPrecordings (Ghaly et al., 1999, 2001). Compared with sufentanil or fentanyl, remifentanilinfusion could always produce stable MEPs with faster emergence (Chung, unpublisheddata).

6. Conclusion

Free-run and stimulated EMG assesses spinal motor nerve roots and determines correctplacement of hardware in cervical, thoracic, and lumbosacral spinal surgeries. BecauseSSEPs and MEPs provide additional information on functional integrity of the spinal cordand nerves, SSEPs and MEPs together with free-run and stimulated EMG should provide

more accurate assessment of spinal cord and nerve function during spinal surgery.

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EMG Methods for Evaluating Muscle and Nerve Function

Edited by Mr. Mark Schwartz

ISBN 978-953-307-793-2

Hard cover, 532 pages

Publisher InTech

Published online 11, January, 2012

Published in print edition January, 2012

InTech Europe

University Campus STeP Ri

Slavka Krautzeka 83/A

51000 Rijeka, Croatia

Phone: +385 (51) 770 447

Fax: +385 (51) 686 166

www.intechopen.com

InTech China

Unit 405, Office Block, Hotel Equatorial Shanghai

No.65, Yan An Road (West), Shanghai, 200040, China

Phone: +86-21-62489820

Fax: +86-21-62489821

This first of two volumes on EMG (Electromyography) covers a wide range of subjects, from Principles and

Methods, Signal Processing, Diagnostics, Evoked Potentials, to EMG in combination with other technologies

and New Frontiers in Research and Technology. The authors vary in their approach to their subjects, from

reviews of the field, to experimental studies with exciting new findings. The authors review the literature related

to the use of surface electromyography (SEMG) parameters for measuring muscle function and fatigue to the

limitations of different analysis and processing techniques. The final section on new frontiers in research and

technology describes new applications where electromyography is employed as a means for humans to

control electromechanical systems, water surface electromyography, scanning electromyography, EMG

measures in orthodontic appliances, and in the ophthalmological field. These original approaches to the use of

EMG measurement provide a bridge to the second volume on clinical applications of EMG.

How to reference

In order to correctly reference this scholarly work, feel free to copy and paste the following:

Induk Chung and Arthur A. Grigorian (2012). EMG and Evoked Potentials in the Operating Room During Spinal

Surgery, EMG Methods for Evaluating Muscle and Nerve Function, Mr. Mark Schwartz (Ed.), ISBN: 978-953-

307-793-2, InTech, Available from: http://www.intechopen.com/books/emg-methods-for-evaluating-muscle-

and-nerve-function/emg-and-evoked-potentials-in-the-operating-room-during-spinal-surgery

intech-emg and evoked potentials in the operating room during spinal surgery (1)

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